Flow sensor

ABSTRACT

A bi-directional flow sensor may be adapted for reducing pneumatic noise during pressure sensing with a flow passing through the flow sensor. The flow sensor may include a hollow, tubular member having a throat section disposed between a ventilator end and a patient end. A flow restrictor may be disposed in the throat section and may be adapted to measure differential pressure in the flow. A baffle may be mounted at the ventilator end and may be adapted to minimize non-axial flow at pressure taps located on opposing ends of the flow restrictor. The patient end may include a flow obstruction configured to promote uniform velocity across the flow at the pressure taps during exhalation flow from the patient end to the ventilator end. The flow sensor can minimize pneumatic noise to less than 0.1 LPM to allow accurate patient flow measurement and triggering of inhalation and exhalation phases at flow rates of 0.2 LPM.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/099,588, filed on Apr. 8, 2008, to issue as U.S. Pat. No. 8,888,711on Nov. 18, 2014, the entire contents of which are hereby incorporatedby reference herein.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND

The present invention relates generally to patient ventilation systemsand, more particularly, to a bi-directional flow sensor having improvedaccuracy in measuring respiratory flow to and from a patient.

Mechanical ventilators are used to provide respiratory support to apatient by assisting in the inhalation and exhalation phases of thebreathing cycle. In one arrangement, the mechanical ventilator may beconnected to the patient by a wye fitting. The wye fitting is, in turn,fluidly connected to the patient's airway by a patient tube connected toa patient interface. The wye fitting may have an exhalation valveconnected to one leg of the wye fitting.

The exhalation valve is moved between open and closed positionsaccording to the phase of the breathing cycle. During the inspirationphase, the exhalation valve is closed to allow compressed gas from theventilator to be delivered to the patient. During the exhalation phase,the exhalation valve opens to allow the patient to exhale to atmosphere.In certain ventilator arrangements, a positive end expiratory pressure(PEEP) valve is used in combination with the exhalation valve in orderto provide an elevated back-pressure above atmosphere during theexhalation phase.

A flow sensor is used to determine the flow rate of compressed gaspassing from the ventilator to the patient as well as determine the flowrate of exhalation gas flowing from the patient to the exhalation valve.Differential pressure detection is one of the more common techniques formeasuring flow of a gas. Differential pressure flow sensors include aflow restrictor positioned within the flow of gas passing through thesensor to allow measurement of the pressure drop (i.e., the differentialpressure) that occurs across the flow restrictor. Bi-directional flowsensors are capable of determining flow rate in either direction as afunction of the measurable pressure difference between upstream anddownstream pressure taps on opposite ends of the flow restrictor. Themeasurable pressure difference is correlated to anempirically-established flow rate.

In some cases, the patient interface is provided as an endotracheal tubefor delivering pressurized gas from the mechanical ventilator to thepatient. The endotracheal tube is typically of a relatively smalldiameter. An airway adapter is used to mate the small diameterendotracheal tube to the larger diameter flow sensor fitting which isavailable in standard sizes. The flow sensor is preferably located asclose to the patient as possible and, in some prior art arrangements,the flow sensor may be incorporated into the wye fitting or may belocated between the wye fitting and the patient interface.

Because of the size discrepancy between the relatively small diameterendotracheal tube and the larger diameter flow sensor, exhalation by thepatient results in a relatively high velocity pressure jet exiting theendotracheal tube and entering the flow sensor. The artificially highvelocity pressure from the endotracheal tube impinges on the pressuretaps of the flow restrictor in the flow sensor. This high velocitypressure jet results in an artificially high differential pressuremeasurement for the given flow relative to the empirically-establishedflow rate/differential pressure relationship. The result is anartificially high flow rate measurement.

In an attempt to overcome the problem of an artificially high flowvelocity generated by the pressure jet, some prior art ventilationsystems increase the distance from the endotracheal tube to the flowsensor by approximately six inches. This increased distance between theflow sensor and the endotracheal tube permits the pressure jet to moreuniformly disperse within the flow sensor prior to impinging upon thepressure taps. In this manner, the flow velocity is relatively constantacross the cross-sectional area of the flow sensor such that pressuremeasurements are believed to be more accurate. Unfortunately, theincrease in distance from the flow sensor to the endotracheal tube alsoincreases the amount of re-breathed volume or deadspace in the patient'sairway. The increased deadspace results in re-breathing of previouslyexhaled gasses.

Another problem associated with flow measurement is that during theinhalation phase, inaccurate pressure measurements at the flow sensorcan occur as a result of pneumatic noise in the flow. Such pneumaticnoise may include turbulence, vibrations, or asymmetric flow conditionsat the ventilator end of the flow sensor (i.e., opposite the patientend). Certain mechanical ventilation systems are configured to operatewith a bias flow which may include pneumatic noise. For example, themechanical ventilator system similar to that disclosed in U.S. Pat. No.6,102,038 issued to DeVries operates with a bias flow which circulatesthrough the wye fitting depending on whether the exhalation valve isopen or closed.

For most applications, the bias flow is typically in the range of about2-10 liters per minute (LPM) and can introduce pneumatic noise at theflow sensor which reduces the accuracy of the flow sensor. The pneumaticnoise in the bias flow may be the product of asymmetric flow conditionsat the inlet to the flow sensor. More specifically, because of thegeometry of the wye fitting, the bias flow may enter the flow sensor ina non-axial direction creating a flow vortex or cross flow at the flowsensor which results in inaccurate pressure measurement at the pressuretaps of the flow sensor.

Pressure sensed in the flow sensor can be used to cycle the mechanicalventilator exhalation valve according to patient-initiated inspirationand exhalation phases of each breathing cycle. Particularly for neonataland pediatric patients, it is desirable to minimize pneumatic noise inthe bias flow such that the 0.2 LPM flow rate at which the inspirationand exhalation phases are triggered, is not disturbed by the pneumaticnoise. In this regard, it is desirable that such pneumatic noise ismaintained at or below 0.1 LPM.

As can be seen, there exists a need in the art for a flow sensor that isadapted for use with neonatal and pediatric patients. More specifically,there exists a need in the art for a flow sensor that can operate withreduced pneumatic noise such that patient-initiated inspiration andexhalation phases of each breathing cycle are triggered at theappropriate flow rate. Additionally, there exists a need in the art fora flow sensor that is adaptable for use with small diameter endotrachealtubes.

Preferably, the flow sensor is configured to eliminate theartificially-high pressure measurement produced by the pressure jetdischarged from the endotracheal tubes during exhalation. Furthermore,it is desirable that the flow sensor is configured to minimize deadspacein order to prevent CO₂ re-breathing by the patient. Finally, thereexists a need in the art for a flow sensor which overcomes the adverseeffects of pneumatic noise at the ventilator end while minimizingresistance to airflow during inspiration and exhalation.

BRIEF SUMMARY

The above-described needs associated with flow sensors for mechanicalventilators is specifically addressed by the present invention whichprovides a bi-directional flow sensor. The flow sensor is adapted foruse with a mechanical ventilator for measuring a flow of compressed gasto a patient during inhalation and exhalation. The mechanical ventilatormay be connected to the patient by means of a conventional wye fitting.The wye fitting may also be fluidly connected to an exhalation valveand/or positive end expiratory pressure (PEEP) valve. The flow sensor isspecifically adapted to limit pneumatic noise to about 0.1 liters perminute (LPM) such that triggering of patient-inspired inspiration andexhalation can occur at about 0.2 LPM. The flow sensor may be integratedinto the wye fitting or provided as a separate component to the wyefitting. The flow sensor may be connected to a patient tube which, inturn, may be connected to a patient interface such as an endotrachealtube.

In its broadest sense, the flow sensor comprises an elongated, hollowtubular member having a flow restrictor for measuring pressuredifferential. The flow sensor may include a baffle at one end of thetubular member and/or a flow obstruction at an opposite end of thetubular member. The baffle is specifically adapted to straightennon-axial flow such as that which characterizes bias flow from themechanical ventilator. The flow obstruction is preferably axial alignedwith the endotracheal tube such that the pressure jet exiting theendotracheal tube during patient exhalation is dispersed into a uniformvelocity profile prior to reaching the flow restrictor wherein theexhalation flow is measured.

The tubular member includes a ventilator end connected to the mechanicalventilator and a patient end connected to the patient airway. Thetubular member may be fitted with a conventional airway adapter havingthe endotracheal tube connected thereto. The tubular member may becylindrically-shaped with a bore defining an interior surface and havinga central axis. The bore may have a reduced cross sectional area at athroat section located between the ventilator end and the patient end.The throat section constricts the exhaled flow entering the patient endprior to the flow reaching the flow restrictor wherein the exhaled flowis measured.

The flow restrictor is diametrically disposed within the throat sectionsuch that the flow restrictor bisects the throat section. In thisregard, the flow restrictor is mounted transversely relative to thecentral axis. The flow restrictor includes a pair of pressure tapsdisposed on axially opposed ends thereof. Each one of the pressure tapsdefines a tap height which is preferably symmetrically disposed aboutthe central axis. Each of the pressure taps is fluidly connected byseparate fluid passageways to a corresponding pair of exterior pressureports.

The pressure ports may be fluidly connected, such as via pressure tubesor fittings, to a pressure transducer to allow conversion of pressuredifferential to flow rate. The sensed pressure is used to measureinspired/expired gas flow. The flow restrictor preferably has asymmetrical aerodynamic cross sectional shape with an aspect ratio thatis aligned with the central axis.

The baffle is disposed within the bore at the ventilator end andcomprises a plurality of vanes which extend radially outwardly from thecentral axis and which are axially aligned with the central axis. Thebaffle is preferably sized and configured to minimize non-axial flow atthe pressure taps. In this regard, the baffle is configured tostraighten the angular nature of the bias flow entering the flow sensor.The bias flow is straightened by the vanes prior to reaching the flowrestrictor wherein pressure differential in the flow is measured andthereafter converted to flow rate. In this regard, the baffle preventscross flow at the flow restrictor in order to increase the accuracy ofpressure measurement.

Each one of the vanes preferably includes a notch formed on a radiallyinward side (i.e., adjacent the central axis) of the baffle at an endthereof opposite the ventilator end. The notches in the vanescollectively define a common pressure relief for the baffle. Thepressure relief is specifically adapted to minimize pressuredifferential between adjacent vane passages (i.e., vane-to-vane pressuredifferential). In this manner, the flow from the ventilator end ispreferably of a uniform velocity profile to ensure accuracy of pressuremeasurement at the flow restrictor.

On an opposite end of the flow sensor, a flow obstruction is disposedwithin the bore between the patient end and the throat section. The flowobstruction is preferably mounted transversely relative to the centralaxis such that the flow obstruction bisects the bore (i.e., isdiametrically disposed therewithin). In addition, the flow obstructionis preferably oriented orthogonally or perpendicularly relative to theflow restrictor when viewed from an axial direction.

Furthermore, the flow obstruction preferably has an aerodynamic crosssectional shape such as a diamond shape or a teardrop shape. The flowobstruction is preferably configured to promote uniform velocity acrossthe bore at the throat section in order to improve the accuracy ofpressure measurement at the pressure taps. The flow obstructionpreferably has an obstruction height that prevents direct impingement ofthe high velocity pressure jet from the endotracheal tube upon thepressure taps which may result in erroneous differential pressuremeasurements.

The flow sensor is specifically adapted for use with a mechanicalventilator and is preferably configured such that pneumatic noise ismaintained at less than 0.1 liters per minute (LPM) in order to allowtriggering of patient-inspired inhalation and exhalation phases of abreathing cycle at a relatively small flow rate of 0.2 LPM as may berequired in neonatal ventilation.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodimentsdisclosed herein will be better understood with respect to the followingdescription and drawings, in which like numbers refer to like partsthroughout, and in which:

FIG. 1 is an exploded perspective view of a flow sensor of the presentinvention and further illustrating an airway adapter fluidly connectingto an endotracheal tube;

FIG. 2 is a perspective view of the flow sensor taken from a patient endthereof;

FIG. 3 is a longitudinal sectional view of the flow sensor illustratinga baffle disposed at a ventilator end, a flow obstruction disposed atthe patient end and a flow restrictor interposed between the baffle andthe flow obstruction;

FIG. 4 a is a longitudinal sectional view of the flow sensor and adapterillustrating the interconnectivity therebetween;

FIG. 4 b is a sectional side view of the flow sensor illustrating ataper section formed in the ventilator end and illustrating therelationship between the flow obstruction and the flow restrictor;

FIG. 5 is a longitudinal sectional top view of the flow sensorillustrating the cross section of the flow obstruction and the axialcross section of the flow restrictor;

FIG. 6 is an end view of the flow sensor at the ventilator endillustrating a plurality of angularly spaced vanes comprising thebaffle;

FIG. 7 is an axial cross sectional view of the flow sensor taken alonglines 7-7 of FIG. 4 b and further illustrating a pressure tap of theflow restrictor;

FIG. 8 is an axial cross sectional view of the flow sensor taken alonglines 8-8 of FIG. 4 b and illustrating an outer circumferential flangeat the patient end;

FIG. 9 is a longitudinal sectional view of the flow sensor illustratingthe flow obstruction at the patient end; and

FIG. 10 is a longitudinal sectional view of the flow sensor illustratinga spiral direction of the flow entering the ventilator end and thestraightening effects of the baffle.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating preferred embodiments of the present invention and not forpurposes of limiting the same, shown in FIGS. 1 and 2 is a perspectiveview of a bi-directional flow sensor 10 specifically adapted for sensingpressure within a flow passing through the flow sensor 10. The flowsensor 10 is shown as being adapted to be interconnected to a patienttube 14 such as an endotracheal tube 16 which may have a relativelysmall size (i.e., small inner diameter 76). The adapter 70 isfrictionally engageable to the flow sensor 10 such as by insertion ofthe adapter 70 into an annular groove 68 formed on one end of the flowsensor 10.

The endotracheal tube 16 may also have a relatively large diameter foruse with adults. Alternative configurations of the patient tube 14 maybe used with the flow sensor other than endotracheal tubes. Regardlessof their specific configuration, the patient tube 14 is adapted toconnect the patient airway to the flow sensor 10. The flow sensor 10 isadapted to facilitate accurate measurement of flow rates passingtherethrough regardless of the patient tube 14 configuration.

The flow sensor 10 includes a flow obstruction 64 at the patient end 26.At each end of the flow obstruction 64 are a pair of pressure taps 44ba, 44 b. The flow obstruction 64 is specifically oriented to be indirect alignment with a high velocity pressure jet discharged from theendotracheal tube 16 during exhalation. In this regard, the flowobstruction 64 is specifically adapted to disperse the pressure jet andpromote a generally uniform velocity across the relatively larger crosssectional area of the flow sensor 10 at the patient end 26 pressure tap44 b. In this manner, the flow obstruction 64 facilitates accuratemeasurement of exhalation flow.

Referring particularly to FIG. 1, the flow sensor 10 may include a pairof fittings 54 sized and configured to engage a corresponding pair ofpressure tube connector 52 openings formed on an exterior side of theflow sensor 10. Each of the pressure tube connectors 52 is fluidlyconnected to a corresponding pressure tap 44 a, 44 b disposed on axiallyopposed ends of a flow restrictor 38. As will be described in greaterdetail below, pressure differential is measured across the pressure taps44 a, 44 b of the flow restrictor 38.

The pressure measurements may be fed to a pressure transducer or otherpressure conversion device by means of a pair of pressure tubesextending from the fittings 54. As is well known in the art, pressuretransducers can be used to determine flow rate such as by using a lookuptable. Flow rate information is used to generate an electrical signalrepresentative of the pressure measurements at the pressure taps 44 a,44 b. The electrical signals may be used to cycle or activate amechanical ventilator 12 (not shown) and an exhalation valve/PEEP valve(not shown) according to patient-initiated inspiration and exhalation atthe appropriate time.

The flow sensor 10 illustrated in FIGS. 1 through 10 has a ventilatorend 24 and a patient end 26. The ventilator end 24 is fluidly connectedto the ventilator 12 such as via a wye fitting (not shown). The flowsensor 10 may be integrated into the wye fitting or may be provided as aseparate component which is fluidly connected to the wye fitting such ason an end thereof adjacent the patient. In this regard, the flow sensor10 may be adapted for use with the mechanical ventilation systemdisclosed in U.S. Pat. No. 6,102,038 issued to DeVries et al., theentire contents of which is expressly incorporated by referencehereinto. The patient end 26 of the flow sensor 10 may be fluidlyconnected to the patient airway such as via the adapter 70/endotrachealtube 16 illustrated in FIGS. 1 and 2. Optionally, the flow sensor 10 maybe integrated into the wye fitting such as the type disclosed in theDeVries reference. The flow sensor 10 and wye fitting may be formed as aunitary structure such as, for example, by injection molding.

The flow sensor 10 is generally configured as an elongated, hollowtubular member 18 having a bore 20 extending therethrough. The bore 20includes an interior surface 28 and defines a longitudinal or centralaxis 22 extending through the bore 20. A baffle 56 may be disposedwithin the bore 20 at the ventilator end 24. The baffle 56 generallycomprises a plurality of vanes 58 which are sized and configured toreduce pneumatic noise by minimizing or straightening non-axial flowinto the ventilator end 24. As was earlier mentioned, the mechanicalventilator 12 may be configured to produce a bias flow which passes fromthe mechanical ventilator 12 into the wye fitting making a significantturn in the wye fitting.

As was earlier mentioned, the bias flow may be a spiral-shaped, twistingflow entering the ventilator end 24 in a non-axial direction. Withoutthe baffle 56, the non-axial bias flow would impinge upon the ventilatorend 24 pressure tap 44 a in a cross flow direction resulting inerroneous differential pressure measurements. Importantly, the baffle 56is specifically sized and configured to reduce or minimize angular orvortex flow entering the bore 20 at the ventilator end 24 such that theflow is axially aligned upon reaching the flow restrictor 38.

Referring to FIG. 3, the flow obstruction 64 can be seen disposed withinthe bore 20 adjacent the patient end 26 of the flow restrictor 38. Aswas earlier mentioned, the flow obstruction 64 is preferably providedwith an aerodynamic cross sectional shape. The flow obstruction 64 isalso preferably positioned to be in general alignment with the pressurejet discharging from the endotracheal tube 16 as best seen in FIG. 9.The flow obstruction 64 promotes uniform velocity across the patient end26 pressure tap 44 b in order to allow accurate pressure measurement ofexhalation flow from the patient.

Referring to FIGS. 4 a to 8, the bore 20 of the tubular member 18 mayinclude a throat section 36 between the ventilator end 24 and thepatient end 26. The throat section 36 can be seen as having a reducedcross sectional area relative to the cross sectional area at theventilator end 24 and/or patient end 26. It should be noted herein thatalthough the tubular member 18 is shown and described as being agenerally cylindrical or hollow tubular member 18, the tubular member 18may be provided in a variety of alternative shapes and configurations.For example, the bore 20 may be provided with a cross sectional shapethat is oval or square or another shape. However, the circular crosssectional shape of the bore 20 is believed to provide favorable flowcharacteristics through the flow sensor and enhance the measurement ofpressure at the flow restrictor 38.

The flow restrictor 38 is diametrically disposed within and bisects thethroat section 36. In this regard, the flow restrictor 38 is mountedtransversely relative to the central axis 22. The flow restrictor 38 ispreferably configured to minimize the generation of turbulence at adownstream side of the flow restrictor 38. As may be appreciated,reference to upstream and downstream ends of the flow restrictor 38 isdependent upon the direction of flow. For example, for flow entering theventilator end 24, the upstream side is closest to the ventilator end 24while the downstream side of the flow restrictor 38 is closest to thepatient end 26.

Conversely, for flow entering the patient end 26 such as from theendotracheal tube 16, the upstream end of the flow restrictor 38 isdisposed adjacent the patient end 26 while the downstream end of theflow restrictor 38 is disposed adjacent the ventilator end 24.Advantageously, the flow sensor 10 is operative to measure flow in twodirections (i.e., bi-directional). The upstream end of the flowrestrictor 38 is the high pressure end while the downstream end is thelow pressure end. The difference in pressure between the upstream anddownstream ends may be correlated to flow rate based on the knownrelationship between the square of flow and differential pressure or itcan be empirically derived.

Referring to FIGS. 4 a and 4 b, the flow restrictor 38 includes a pairof pressure taps 44 a, 44 b on opposed ends of the flow restrictor 38.Each pressure tap 44 a, 44 b is defined as a generally open orifice orgroove formed along axially opposed ends of the flow restrictor 38. Thepressure taps 44 a, 44 b are fluidly connected by a corresponding pairof fluid passageways 48 to a pair of exterior pressure ports 50 on anouter wall of the tubular member 18. As can be seen in FIG. 7, the fluidpassageways 48 extends upwardly from the pressure taps 44 a, 44 b to thepressure ports 50 wherein a fittings 54 fluidly communicate the pressureat the pressure taps 44 a, 44 b to the pressure transducer. As best seenin FIG. 4 b, each of the pressure taps 44 a, 44 b defines a tap height46 which is preferably symmetrically disposed about the central axis 22of the bore 20 and which is also preferably equal to or less than anobstruction height 66 of the flow obstruction 64.

Referring briefly back to FIG. 5, the flow restrictor 38 preferably hasan aerodynamic shape in order to minimize disruptions in the flow. Forexample, the flow restrictor 38 is preferably provided with an oblongshape such as a diamond, oval or other suitable cross sectional shape tominimize the generation of turbulence in the flow which may reduce theaccuracy of pressure measurements as well as increase the resistance toflow.

Referring to FIGS. 2, 3, 4 b and 6, shown is the baffle 56 disposedwithin the bore 20 at the ventilator end 24. As can be seen, the baffle56 comprises a plurality of vanes 58 which extend radially outwardlyfrom the central axis 22. Each of the vanes 58 may be generally axiallyaligned with the central axis 22. The vanes 58 extend radially outwardlyfrom the central axis 22 to the interior surface 28 of the bore 20. Thebaffle 56 is preferably sized and configured to minimize non-axial flowat the pressure taps 44 a, 44 b. In this regard, the baffle 56straightens angular or vortex flow entering the flow sensor 10.

The baffle 56 is specifically adapted to minimize cross flow at the flowrestrictor 38 which can otherwise result in erroneous pressuredifferential measurements. Although eight vanes 58 are shown, the baffle56 may comprise any number of vanes 58. For example, the baffle 56 maycomprise a pair of diametrically opposed vanes 58 which collectivelybisect the bore 20 at the ventilator end 24. Alternatively, the baffle56 may comprise four of the vanes 58 which are preferably orientedorthogonally (i.e., 90°) relative to one another. Most preferably, thebaffle 56 comprises eight of the vanes 58 as illustrated in the figureswherein each of the vanes 58 is equally angularly spaced relative to oneanother.

Referring particularly to FIG. 4 b, the bore 20 may include a tapersection 30 located adjacent the baffle 56 wherein the bore 20 tapersradially inwardly along a direction from the ventilator end 24 towardthe throat section 36. In this regard, flow entering the ventilator end24 is constricted as it flows toward the throat section 36. The tapersection 30 may be a single taper section disposed between the extremeends of the bore 20 or the taper section 30 may be comprised ofprogressively steeper first and second tapers 32, 34.

In one embodiment best seen in FIG. 4 b, the first taper 32 may have ahalf angle (i.e., relative to the central axis 22) of up toapproximately 2° as indicated by the reference character θ₁. The secondtaper 34 is disposed axially inwardly from the first taper 32 andpreferably has a half angle, indicated by the reference character 02, ofbetween approximately 12° and approximately 16° (relative to the centralaxis 22). Transitions between the first and second tapers 32, 34 and thethroat section 36 are preferably with a smooth radius in order to avoiddisruption in the flow which may generate noise-producing eddies orturbulence.

Each one of the vanes 58 preferably includes a notch 60 formed on aradially inward side (i.e., along the central axis 22) and opposite theventilator end 24. The formation of the notch 60 may be generallylocated in the area of the second taper 34 of the bore 20 and allowslocalized high pressure in any one of the vane 58 passages to berelieved by discharging of any differential (i.e., vane-to-vane)pressure. In this regard, the pressure relief 62 reduces the amount ofpneumatic noise and cross flow in the area of the pressure taps 44 a, 44b to improve pressure measurement accuracy.

Referring still to FIG. 4 b, shown is the flow obstruction 64 interposedbetween the patient end 26 and the flow restrictor 38. The flowobstruction 64 is mounted transverse to the central axis 22 but isoriented perpendicularly relative to the flow restrictor 38 when viewedfrom an axial direction. The flow obstruction 64 bisects the bore 20 andpreferably has an aerodynamic cross sectional shape in a transversedirection. The shape preferably has an aspect ratio aligned with thecentral axis 22. The aerodynamic cross sectional shape may be a diamondshape as illustrated in the figures or any other alternative shape. Forexample, the flow obstruction 64 may be provided with a teardrop axialcross section wherein the leading edge of the teardrop faces the patientend 26 and the trailing edge of the teardrop faces the ventilator end24.

It is further contemplated that when viewed in an axial direction, theflow obstruction 64 and flow restrictor 38 are aligned with one another.However, a more preferable relationship is that which is illustrated inthe figures wherein the flow obstruction 64 is oriented orthogonally orperpendicularly relative to the flow restrictor 38 when viewed in anaxial direction. Such an arrangement has been proven to promote betteruniformity in the flow velocity across the cross section of the bore 20.

Referring particularly to FIGS. 4 b and 9, the flow obstruction 64defines an obstruction height 66. The obstruction height 66 ispreferably at least equivalent to the tap height 46 of each one of thepressure taps 44 a, 44 b such that the pressure jet discharged from theendotracheal tube 16 as shown in FIG. 9 is dispersed into a more uniformvelocity profile rather than a direct high velocity pressure jetimpinging on the pressure taps 44 a, 44 b. As was earlier mentioned, thehigh velocity pressure jet at the pressure taps 44 a, 44 b wouldotherwise result in inaccurate flow measurements. It is alsocontemplated that the obstruction height 66 may be greater than the tapheights 46 of the pressure taps 44 a, 44 b.

Referring briefly to FIG. 8, shown is an axial cross sectional view ofthe flow sensor 10 at the patient end 26 and which illustrates anannular groove 68 formed at the patient end 26 for engagement to astandard-sized adapter 70. As was earlier mentioned, such adapter 70 maybe a commonly-available airway adapter 70 used for attaching varioussize patient tubes (i.e., endotracheal tubes 16) to the flow sensor 10.As can be seen in FIG. 4 b, the adapter 70 includes a cylindricalextension 72 which is sized and configured to frictionally engage theannular groove 68.

In operation, during a patient-inspired inhalation phase, flow (e.g.,such as bias flow) from the mechanical ventilator 12 enters theventilator end 24 as best seen in FIG. 10. The bias flow may includepneumatic noise such as vibrations, turbulence or asymmetric flowinduced by the curved flow path from the mechanical ventilator into thewye fitting. Flow from the mechanical ventilator 12 passes through thevanes 58 which extend radially outwardly from the central axis 22.

As was earlier mentioned, the vanes 58 are preferably sized andconfigured to straighten non-axial flow at the pressure taps 44 a, 44 bin order to ensure accurate pressure measurement. The pressure relief 62collectively formed by the notches 60 in the vanes 58 is specificallysized and configured to discharge or equalize any differential pressurebetween the vanes 58 prior to the flow reaching the flow restrictor 38.The flow then passes to the patient via the endotracheal tube 16 such asthat which is illustrated in FIG. 4 a.

During the exhalation phase, expired gas is discharged as a highpressure jet from the endotracheal tube 16 as shown in FIG. 9. The highpressure jet enters the flow sensor 10 at the patient end 26 whereuponthe flow obstruction 64 causes dispersion of the flow. The flowobstruction 64 preferably has a height which is at least equal to thetap height 46 of each of the pressure taps 44 a, 44 b on the flowrestrictor 38 to minimize or eliminate direct impingement of thepressure jet from the endotracheal tube 16 upon the pressure taps 44 a,44 b. This geometric relationship between the obstruction height 66 andthe tap height 46 prevents an artificially high flow rate measurement.

Instead, the flow obstruction 64 promotes a uniform velocity profileacross the bore 20 at the pressure taps 44 a, 44 b for the flow passingfrom the patient end 26 and exiting the ventilation end. Advantageously,the flow obstruction 64 allows for a flow sensor 10 configuration whichreduces deadspace at the patient interface. As was previously mentioned,excessive deadspace is especially undesirable in mechanical ventilation.

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the inventiondisclosed herein. Further, the various features of the embodimentsdisclosed herein can be used alone, or in varying combinations with eachother and are not intended to be limited to the specific combinationdescribed herein. Thus, the scope of the claims is not to be limited bythe illustrated embodiments.

What is claimed is:
 1. A bi-directional flow sensor for sensing pressureof a flow passing therethrough, the flow sensor comprising: a hollowtubular member having a ventilator end and a patient end and defining abore with a central axis, the bore including a throat section disposedbetween the ventilator end and the patient end; a flow restrictorbisecting the throat section and including a pair of pressure taps eachdefining a tap height; and a flow obstruction disposed at the patientend and being configured to promote uniform velocity across the bore atthe pressure taps.
 2. The bi-directional flow sensor of claim 1, whereinthe pair of pressure taps are disposed on opposite ends of the flowrestrictor.
 3. The bi-directional flow sensor of claim 2, wherein thetap height of each pressure tap of the pair of pressure taps issymmetrical about the central axis.
 4. The bi-directional flow sensor ofclaim 3, wherein the tap height of the pressure tap disposed on the endof the flow restrictor facing the patient end has a height that is equalto or less than an obstruction height of the flow obstruction.
 5. Thebi-directional flow sensor of claim 2, wherein each pressure tap of thepair of pressure taps is defined as a generally open orifice formedalong axially opposed ends of the flow restrictor with respect to thecentral axis.
 6. The bi-directional flow sensor of claim 2, wherein thepair of pressure taps are fluidly connected by a corresponding pair offluid passageways to a corresponding pair of external pressure ports. 7.The bi-directional flow sensor of claim 1, wherein the flow restrictorhas a symmetrical aerodynamic cross sectional shape.
 8. Thebi-directional flow sensor of claim 7, wherein the symmetricalaerodynamic cross sectional shape has an aspect ratio that is alignedwith the central axis.
 9. The bi-directional flow sensor of claim 1,wherein the flow obstruction bisects the bore transverse to the centralaxis.
 10. The bi-directional flow sensor of claim 9, wherein the flowobstruction has a symmetrical aerodynamic cross sectional shape.
 11. Thebi-directional flow sensor of claim 10, wherein the symmetricalaerodynamic cross sectional shape has an aspect ratio that is alignedwith the central axis.
 12. The bi-directional flow sensor of claim 1,further comprising: a baffle disposed within the bore at the ventilatorend and comprising a plurality of vanes, the baffle being sized andconfigured to minimize non-axial flow at the pressure taps.
 13. Thebi-directional flow sensor of claim 12, wherein the baffle is configuredto minimize cross flow at the flow restrictor.
 14. The bi-directionalflow sensor of claim 12, wherein the baffle comprises a pair ofdiametrically opposed vanes which collectively bisect the bore at theventilator end.
 15. The bi-directional flow sensor of claim 12, whereinthe baffle comprises four vanes oriented orthogonally relative to oneanother.
 16. The bi-directional flow sensor of claim 12, wherein each ofthe plurality of vanes is radially oriented and includes a notch on aradially inward side proximal to the central axis such that the notchescollectively define a pressure relief area within the bore.
 17. Thebi-directional flow sensor of claim 12, the bore includes a tapersection located adjacent the baffle such that the bore tapers radiallyinwardly along a direction from the ventilator end toward the throatsection.
 18. A bi-directional flow sensor for sensing pressure of a flowpassing therethrough, the flow sensor comprising: a hollow tubularmember having a ventilator end and a patient end and defining a borewith a central axis, the bore including a throat section disposedbetween the ventilator end and the patient end; a flow restrictorbisecting the throat section and including a pair of pressure taps eachdefining a tap height; and a baffle disposed within the bore at theventilator end and comprising a plurality of vanes, the baffle beingsized and configured to minimize non-axial flow at the pressure taps.19. The bi-directional flow sensor of claim 18, further comprising: aflow obstruction disposed at the patient end and being configured topromote uniform velocity across the bore at the pressure taps.
 20. Anapparatus comprising: a hollow tubular member having a first end and asecond end and defining a bore with a central axis, the bore including athroat section disposed between the first end and the second end; a flowrestrictor bisecting the throat section and including a pair of pressuretaps each defining a tap height; a flow obstruction disposed at thesecond end and being configured to promote uniform velocity across thebore at the pressure taps; a baffle disposed within the bore at thefirst end and comprising a plurality of vanes, the baffle being sizedand configured to minimize non-axial flow at the pressure taps; and anadapter comprising an extension member being configured to frictionallyengage with the second end.